LISLE, ILLINOIS--Wild orangutan populations have crashed by half in the last 7 years, according to a new estimate presented here today at an international ape research meeting. Experts say orangutans could soon be extinct in the wild if the trend continues. They blame the drop mostly on intensive logging and huge forest fires that have destroyed the animals' habitat.

Orangutans, the third-closest living relative to humans, once lived in vast forests on the large islands of Borneo and Sumatra, in Indonesia and Malaysia. Those habitats remained mostly intact until the early 1990s, when logging--both legal and illegal--and forest fires became much more common.

To gauge the decline, Carel van Schaik of Duke University and his colleagues estimated orangutan populations in a section of the 9000-square-kilometer Leuser National Park on Sumatra in 1993 and 1999, using a combination of satellite imaging and aerial photos of the animals' habitat, combined with knowledge from 24 years of field work. The survey showed that populations in the park had dropped from 12,000 to 6500. The world population, according to another estimate published last year, was 27,000 in 1998.

The loss is especially severe because van Schaik and other researchers have only just begun to chart the apes' primitive culture, which varies from population to population. Much of that may forever be lost, he says. There are a few rays of hope, however; the Indonesian press is paying more attention recently, and Indonesia's new government has begun prosecuting illegal loggers. "That has put the fear of God into people," van Schaik says.

The survey is "likely to be accurate, and it's great reason to be horrified," says Cambridge University primatologist David Chivers. After El Niño, the ensuing drought, and the fires of 1997 and 1998, researchers were already expecting the worst, he says. If present trends continue, Chivers gives the apes another 20 years at most: "If this is not stopped, the orangutan is going to be extinct."